1. Field of the Invention
This invention relates to offshore gas flares and more particularly to apparatus for igniting waste gas for combustion at a location spaced from an offshore well.
2. Description of the Prior
It has heretofore been proposed as in U.S. Pat. No. 1,087,112, to burn gas on the surface of the water released below the surface through a nozzle carried on a buoy. In order to ignite the gas a lump of potassium, sodium or calcium phosphid is released from below the water surface by the pressure of the fuel, rises to the surface of the water and ignites to ignite the gas. Only a single ignition is intended, or possible, combustion being maintained by continuous supply of gas.
Flares for offshore use and capable of accommodation to changes of depth due to wind, tides and the like are shown in U.S. Pat. No. 2,894,269 to Dodge; U.S. Pat. No. 3,652,196 to Marion et al.; U.S. Pat. No. 3,666,395 to Kubasta; U.S. Pat. No. 3,902,843 to Genini et al.; and U.S. Pat. No. 3,920,378 to Castela.
Of these only Castela et al. in U.S. Pat. No. 3,920,378, undertake to provide a lighting device which is shown only diagrammatically and is described only as of the type producing electrical impulses to produce sparks at the level of the night lights and which apparently require the intervention at the flare of a workman for actuating the lighting circuits. Reference is also made to the intended use of a fuse on FIG. 1 but this is not otherwise shown nor described.
Lapp, in U.S. Pat. No. 4,025,281, has only a pilot system and no automatic or remote control means for the pilot gas. The pilot gas is manually adjusted by valve 104 and flows continuously without adjustment automatically or remotely. The pilot and ignitor system of Lapp differs greatly from the system of applicant in that it is essential in Lapp to set up the system with the proper continuous pilot gas flow and thereafter effect the ignition automatically.
Lapp's igniter utilizes a flame front propagated through a pipe to the pilot. The use of a flame front is wholly unsuited for transmission through a pipe submerged in ocean water. The flame front itself produces water vapor which would condense in a submerged ocean water cooled pipe and tend to block the pipe with repeated propagation, even if both the air and gas to produce the flame front were essentially water free. Lapp recognized the problems attendant upon cooling of the pipe through which the flame is advanced (See column 3, line 61 through column 4, line 21). The present invention uses an entirely different approach, does not advance a flame through a subsea pipe but merely transmits fuel gas which can be dried and establishes the flame front at the flare itself.
Kubasta, in U.S. Pat. No. 3,666,395 makes no provision for a pilot or for igniting a pilot but indicates (column 3, line 74 and following) that a ladder may extend to the burner tip for lighting the same.
British Pat. No. 1,244,273, to Mobil Oil Corporation shows a semi-submersible drilling vessel 32 with a drill string 30, a plurality of subsea production satelite systems 10, each serving a plurality of subsea wellheads 14, with shipping lines 18 extending therefrom to a storage tank 17. A floating master station 20 is provided connected to the tank 17 through a tethered tension pipe 22 with a large subsurface buoy 24 at its upper end. The master station 20 has power generating and final stage separation equipment as well as offloading apparatus. A flexible conduit 26 connects the master station 20 to the tethered tension pipe 22 and is provided with a plurality of electrical and fluid flow paths, the electrical connections apparently supplying energy to the satelite stations 10 and the fluid flow paths transferring fluid from the tether pipe 22 to the master station 20 for final stage separation.
It is indicated (page 6, line 95 and following) that the separated gas can be utilized, stored, or disposed of at the site, by flaring (line 112). If the gas is to be flared (lines 121 and 122) a flare stack is erected above the master station 20. No details of the flare stack are described.
It is not particularly desireable to locate a flare stack continguous to oil separation and offloading equipment and the structure of this British patent bears little resemblance to transferring gas for flaring from an offshore platform to a separated flare.
If the flow of gas to be burned to an offshore flare is continuous, a single ignition may be adequate but if the flow is interrupted then difficulties are encountered. Various expedients have been resorted to for ignition of offshore flares including the use of Roman candles, flare pistols, and tracer bullets but these have not proven satisfactory.
Hazards to personnel, because of combustible liquid carryover, vapor clouds and high radiation from burning flares add to the problem.
It has been common practice to ignite flares supported above the ground by the use of flame fronts to ignite gas fired pilots. My prior U.S. Pat. No. 3,816,059 shows such a system. These are not feasible with offshore flares because of chilling of the flame carrying pipe by the surrounding water and condensate build-up in subsea pipes.